Tech Tuesday: Valves and Camshafts
Introduction You might have seen badges on some cars that say "32V" or "DOHC", or perhaps an advertisement from a manufacturers that claim improvements on their engines from those things. In this (inaugural) Tech Tuesday article, we're going to explain what they mean. In order of sophistication, there are 4 types of camshaft and valve formations: flathead, pushrod (or OHV), SOHC, and DOHC. The number of valves in an engine is usually related to the camshaft formation, but it can vary between engine manufacturers. Valves Camshafts Flathead This involves intake and exhaust valves that are level with the top of the cylinder, leading to a "flat" cylinder head. The camshaft is sometimes deep down in the engine block, actuating the valves via rods, but it can also sit directly under or beside the valves. the This configuration has not been used in passenger cars for decades, due to the advent of more advanced engine technologies. Pros * Cons * Pushrod (or OHV) This stands for Overhead Valves, involves one camshaft with intake and exhaust lobes above each cylinder bank, using rods pushed by the lobes to actuate the valves (now above the cylinders). Again, the camshaft is usually deep down in the engine block. This configuration is used in some diesel trucks, and the well-known LS and LT engines in the C5-C8 Chevrolet Corvette. Pros * If the cylinder head is damaged, only the valves and/or pushrods are damaged, not the whole camshaft * The belt or chain used to run the camshaft can be shorter, as the camshaft is next to the crankshaft * High reliability and damage resistance * Relatively cheap to produce Cons * Camshaft is deep down in engine, harder to access * Pushrods need oil and maintenance as well SOHC This stands for Single Overhead Camshaft, and involves one camshaft with intake and exhaust lobes above each row of cylinders. Like the pushrod engine, the valves are also above the combustion chamber. This configuration was popular up until recently, with Honda being one of the last to use it in their passenger cars. Pros * Cheaper than DOHC to produce * Easier access versus flathead and pushrod configurations * If the camshaft breaks, you only need to replace one * Very reliable, as it has less moving parts than a pushrod configuration Cons * More complicated than DOHC, as one cam does double the work * Camshaft is more expensive to replace, as it has more lobes and is more intricate * Being inside the cylinder head, the camshaft will need replacing if the head or valvetrain is damaged DOHC This stands for Double Overhead Camshaft, and uses two camshafts above each cylinder bank: one for the intake valves, and one for the exhaust. This configuration is used in the overwhelming majority of mainstream cars, and automobiles in general. Pros * Intake and exhaust strokes can be fine-tuned more easily * Less complicated than an SOHC * Very fuel-efficient * Can handle high horsepower figures Cons * Same damage risk as an SOHC configuration, only two camshafts will need replacing * Still pretty complicated * Relatively high production cost Category:Tech Tuesdays Category:StayLexusLFA